This study established a method for simultaneous determination of capsaicin and dihydrocapsaicin in the placenta of Jingjiao 1 by ultra high performance liquid chromatography（UPLC）, and detected the dynamic changes in the accumulation of capsaicin and dihydrocapsaicin content. The determined chromatographic conditions were the mobile phase of methanol vs water（70∶30） with a flow rate of 1.0 mL/min and an Eclipse XDB-C₁₈ column（50mm×2.1 mm, 1.8 μm）, column temperature is 30 ℃, injection volume is 1 μL. The running time was 5 min. The results showed that the retention times of capsaicin and dihydrocapsaicin were 0.8 min and 1.1 min, respectively, with good linear relationships within the selected range. The average spiked recovery rates were 98.2% and 105.5%, and the RSD was 2.24% and 3.15%. The content of capsaicin and dihydrocapsaicin in Jingjiao 1 showed fluctuating increases, with the highest points occurring 40 days after flowering. The UPLC method was easy to operate, had good separation effect and repeatability, and was fast and accurate. It can be used as an accurate quantitative method for capsaicin and dihydrocapsaicin.